1. Field of the Invention
The present invention relates to an energy recycling device and, more particularly, to a motor energy recycling device, which is capable of recycling the not-used energy released from magnetic field changes when the motor controlled by pulse width modulation.
2. Description of Related Art
With reference to FIGS. 1A and 1B, FIG. 1A illustrates the control circuit for a typical DC motor, and FIG. 1B illustrates the control circuit for a typical three phase AC motor. As shown in FIG. 1A, the control circuit includes a voltage regulating power capacitor 10, a switch unit 11, and a diode 12. The voltage regulating power capacitor 10 supplies power to a DC motor 91. The switch unit 11 controls power supply to the DC motor 91. The diode 12 is preferably a flywheel diode. When the switch unit 11 is off, the control circuit maintains a current loop of the DC motor 91 so as to convert the energy stored in a magnetic field of the DC motor 91 into electric power. Further, the electric power passed through the diode 12 and is changed into a thermal energy to dissipate. As shown in FIG. 1B, the three phase AC motor has a first phase 921, a second phase 922, and a third phase 923 with a phase difference of 120-degree therebetween. The control circuit includes a voltage regulating power capacitor 10, a switch unit 11, and six diodes 12. The voltage regulating power capacitor 10 supplies power required for the first phase 921, the second phase 922, and the third phase 923 respectively. The switch unit 11 includes six switches 111 to control the first phase 921, the second phase 922, and the third phase 923 to be in or out, respectively, in order to configure the three phase AC motor into a one-in/two-out or two-in/one-out mode to thereby form a loop for running the three phase AC motor. The diodes 12 each is preferably a flywheel diode.
Typically, in a pulse width modulation (PWM) operation, a pulse signal is used as an input current to control the power of the motor. As shown in FIGS. 1A and 1B, the control circuit of the pulse width modulation can turn on/off the switches 11 continuously based on an appropriate operating frequency. By adjusting the ratio of on-time and off-time of the switch unit 11, it is able to adjust the input energy of the DC motor 91 or the three phase AC motor.
When the motors are controlled in such a way, the motors are kept in a cycle of increasing and decreasing of magnetic fields. When the magnetic field is decreased, the energy released by the motor is consumed by the diodes 12 in a form of heat. In this case, in every cycle of on/off of the switch unit 11, the energy released by the motor is wasted.
To overcome this, a capacitor is typically added over the diodes to thereby store the energy released by the motor, and the energy stored in the capacitor can reversely charge the power capacitor immediately. Thus, when the capacitor performs a reverse energy charging, the voltage of the power capacitor instantaneously increases, and the rotating speed of the motor is increased sharply, which may cause vibration of the motor and result in a security problem or a difficulty in control of the motor. In addition, the energy stored in the capacitor can be expressed as ½CV2, where C is the capacitance of the capacitor and V is the voltage of the capacitor. If the voltage of the capacitor cannot be accumulated to a certain high value, a relative large amount of energy may be consumed by the recycling circuit during the energy recycling process, resulting in severely reducing the recycling performance.
Therefore, it is desirable to provide an improved motor energy recycling device to mitigate and/or obviate the aforementioned problems.